Elements & Uses of NPK Fertilizer

Nutrient Balance

• NPK fertilizers are made in different combinations of elements, denoted by the numbers that accompany the letters. For example, a bag of 10-10-10 fertilizer contains 10 percent nitrogen, 10 percent phosphorus and 10 percent potassium. Some mixtures are made up of more nitrogen than phosphorus. A blend of 20-5-5 contains 20 percent nitrogen but only 5 percent of each other element. Sometimes, potassium is identified as potash, but they are the same element. A high concentration of one element may be just as damaging to soil as not enough. Use pH tests to learn if your soil is lacking in one or more elements, and buy an appropriate fertilizer mixture to balance out of the levels.

Nitrogen

• Nitrogen is the element that's primarily responsible for leaf production in plants. Soil is naturally composed of nitrogen, but plants leach it out as they grow. Grasses and leaf-bearing vegetables feed heavily on nitrogen. Look for stunted, weak stems and yellow leaf discoloration that indicate a nitrogen deficiency is present in the soil. Nitrogen washes out of soil when rain is present, and fertilizers are used to replace this needed soil element.

Phosphorus

• Phosphorus is essential in helping plants develop roots and germinate from seed, and young plants feed on it heavily during early growth stages. Carrots, turnips and other root vegetables use copious amounts of phosphorus. When phosphorus deficiencies are present in soil, leaves may look purplish and growth will be stunted. Unlike nitrogen, which washes out with rain, phosphorus stays in the ground for many years. Generally, this element is applied to soil only once a year, early in the growing season.

Potassium

• Potassium is necessary for flower and fruit production, and it helps plants remain disease resistant. Vegetables, fruits and flowering plants all use potassium. Leaf scorch and poor-quality fruit are common indicators of potassium deficiency in soil. Tomatoes are particularly affected by a lack of potassium. The element lingers in the soil for years, but vegetables feed on it heavily, so frequent fertilizer applications may be necessary.